Background The reasons for discordance between advance care planning (ACP) documentation and current preferences are not well understood. The POLST form offers a unique opportunity to learn about the reasons for discordance and concordance that has relevance for POLST as well as ACP generally. Design Qualitative descriptive including constant comparative analysis within and across cases. Setting Twenty-six nursing facilities in Indiana. Participants Residents (n = 36) and surrogate decision-makers of residents without decisional capacity (n = 37). Measurements A semi-structured interview guide was used to explore the reasons for discordance or concordance between current preferences and existing POLST forms. Findings Reasons for discordance include: (1) problematic nursing facility practices related to POLST completion; (2) missing key information about POLST treatment decisions; (3) deferring to others; and (4) changes over time. Some participants were unable to explain the discordance due to a lack of insight or inability to remember details of the original POLST conversation. Explanations for concordance include: (1) no change in the resident's medical condition and/or the resident is unlikely to improve; (2) use of the substituted judgment standard for surrogate decision-making; and (3) fixed opinion about what is "right" with little to no insight. Conclusion Participant explanations for discordance between existing POLST orders and current preferences highlight the importance of adequate structures and processes to support high quality ACP in nursing facilities. Residents with stable or poor health may be more appropriate candidates for POLST than residents with a less clear prognosis, though preferences should be revisited periodically as well as when there is a change in condition to help ensure existing documentation is concordant with current treatment preferences.